Nanopore Diffusion Rates for Adsorption Determined by Pressure-Swing and Concentration-Swing Frequency Response and Comparison with Darken's Equation

Abstract

Two flow-through frequency response methods of concentration-swing frequency response (CSFR) and pressure-swing frequency response (PSFR) are applied to study the adsorption of chloroethane on BPL activated carbon over a wide range of concentrations. Chloroethane at low concentrations in helium, 500 ppm V and 10 mol %, are studied using CSFR. Two models which treat an adsorption bed with axial dispersion or a simplified well-mixed concentration have been developed for both isothermal and nonisothermal conditions. The results show that heat effects can be negligible for the CSFR method. Pure chloroethane at relatively high concentrations is studied using PSFR. The experimental data are described well by a nonisothermal nanopore diffusion model. The diffusivities obtained from these two distinct methods are identical for the same concentration. The modeling of the concentration behavior depends quite sensitively on the isotherm model and obeys Darken's equation for the D-R isotherm. The results show that the frequency response method can distinguish the importance of heat effects and the relative importance of the mass-transfer mechanisms.

New development in flow‐through pressure‐swing frequency response method for mass‐transfer study: Ethane in ZIF‐8

“…In addition to studies in batch systems, there are other applications in flow‐through systems involving perturbation in flow rate, concentration, or pressure . Flow‐through FR methods have been explored to provide more practical advantages, such as easily implementing a wide range of frequencies, having the possibility of using large relative amplitudes, and having reduced heat effects .…”

“…However, it has limitation on the maximum frequency, which cannot exceed ∼1 Hz, whereas the maximum frequency in a batch system can go up to 100 Hz. Most recent work using such flow‐through techniques has been developed by LeVan and coworkers on pressure‐swing FR (PSFR) and concentration‐swing FR (CSFR) methods that have been used to study mass‐transfer rates for both pure and mixed gases and vapors for various adsorbents: carbon molecular sieves, silica gels, zeolites, metal‐organic frameworks (MOF), and activated carbon materials . Given that each technique has its own advantages and disadvantages, a combined FR apparatus that can perform VSFR, PSFR, and CSFR experiments has been built to be applied to a wider frequency range than VSFR or PSFR alone.…”

Master curves for mass transfer in bidisperse adsorbents for pressure‐swing and volume‐swing frequency response methods

“…Mass‐transfer rates for these four pure components have been measured at 25°C and 1 bar using the PSFR method. Detailed information is given elsewhere 31, 35. Figure 11 shows the experimental data and the best fit for CH 4 , N 2 , O 2 , and CO 2 .…”

“…Furthermore, heat effects have been shown to be often negligible for CSFR but often apparent for PSFR because of operating conditions. Axial dispersion has been considered and can be easily recognized by the CSFR method 31…”

“…Thus, it is possible to develop maps of rate parameter values by varying the concentration and temperature about which the perturbations are performed. This has been done previously4, 8, 20, 22, 31, 35, 40–45 and permits comparison with theoretical trends predicted by Maxwell‐Stefan, Darken, Arrhenius, and other models as well as molecular simulation.…”